Adaptive linearization technique for communication building block

Abstract

The present invention is directed to a linearization apparatus and method. Preferred embodiments according to the present invention can combine an auxiliary non-linear block to a functional block of a system to increase linearity of an output signal of the system such as a communication system. System overhead due to the non-linear auxiliary block can be small because of circuit structure, cost and low consumption. Further, the non-linear auxiliary block can be designed so that no feedback path is required. Further preferred embodiments can use a feedback path without loss of stability by using a cancellation apparatus or process based on an averaging detection of the output signal. For example, a feedback loop can detect power leakage in a sideband caused by non-linearities of the communication system.

1. A circuit for linearizing an input signal x(t), comprising:
 a main circuit that receives the input signal with a main transfer function of approximately H1 and outputs a main signal output; 
 a nonlinear auxiliary circuit that receives the input signal and has a nonlinear auxiliary transfer function of approximately H2 and outputs a nonlinear auxiliary signal output, wherein H 1 (X)=a 1 X+a 3 X 3  and H 2 (X)=b 1 X+b 3 X 3  and X is the transform of x(t), a 1 xa 3 <0, b 1 xb 3 <0, a 1 −a 3  is approximately a 1 , and b 1 −b 3  is approximately 0; and 
 a combiner coupled to said main circuit and said nonlinear auxiliary circuit that combines said main signal and said auxiliary signal to yield an output signal. 
 
   
   
     2. The circuit of  claim 1 , further comprising a feedback loop coupled to said combiner. 
   
   
     3. The circuit of  claim 2 , wherein said feedback loop comprises a bandpass filter. 
   
   
     4. The circuit of  claim 3 , wherein said feedback loop further comprises a gain stage. 
   
   
     5. The circuit of  claim 2 , wherein said feedback loop further comprises a power detector. 
   
   
     6. The circuit of  claim 2 , wherein said feedback loop further comprises a threshold detector. 
   
   
     7. The circuit of  claim 2 , wherein said feedback loop further comprises:
 a bandpass filter coupled to the combiner that receives the output signal; 
 a gain stage coupled to receive an output of the bandpass filter; 
 a power detector coupled to receive an output of the gain stage; and 
 a threshold detector coupled to receive an output signal of the power detector, wherein an output of the threshold detector is received by the nonlinear auxiliary circuit. 
 
   
   
     8. The circuit of  claim 7 , further comprising a mixer coupled to an input of the bandpass filter. 
   
   
     9. The circuit of  claim 1 , further comprising a feedback loop, wherein said feedback loop receives a portion of the output signal and outputs a non-linearity control signal to said auxiliary nonlinear circuit. 
   
   
     10. The circuit of  claim 9 , further comprising a non-linearity detector that detects the amount of non-linearity in the output signal, wherein the non-linearity control signal is based on the amount of non-linearity detected by said non-linearity detector. 
   
   
     11. The circuit of  claim 10 , wherein said nonlinear auxiliary circuit increases a power level of said nonlinear auxiliary output signal in proportion to the non-linearity control signal. 
   
   
     12. The circuit of  claim 9 , further comprising a non-linearity detector that detects the amount of non-linearity in the output signal, wherein the non-linearity feedback signal is proportional to the amount of non-linearity detected by the nonlinear detector. 
   
   
     13. The circuit of  claim 12 , wherein said feedback loop further comprises:
 a bandpass filter coupled to the combiner that receives the output signal; 
 a gain stage coupled to receive an output signal of the bandpass filter; 
 a power detector coupled to receive an output signal of the gain stage; and 
 a threshold detector coupled to receive an output signal of the power detector, wherein an output of the threshold detector is received by the nonlinear auxiliary circuit. 
 
   
   
     14. The circuit of  claim 9 , wherein said main circuit comprises a linearization circuit. 
   
   
     15. The circuit of  claim 1 , wherein said main circuit comprises a linearization circuit. 
   
   
     16. The circuit of  claim 15 , further comprising a feedback loop, wherein said feedback receives a portion of the output signal and outputs a non-linearity feedback signal to said nonlinear auxiliary circuit. 
   
   
     17. The circuit of  claim 16 , wherein said feedback loop further comprises a nonlinearity detector that detects the amount of non-linearity in the output signal, wherein the nonlinearity feedback signal is proportional to the amount of non-linearity detected by the non-linearity detector. 
   
   
     18. The circuit of  claim 17 , wherein said nonlinear auxiliary circuit increases a power level of said nonlinear auxiliary output signal in proportion to the non-linearity feedback signal. 
   
   
     19. The circuit of  claim 18 , wherein said feedback loop further comprises:
 a bandpass filter coupled to the combiner that receives the output signal; 
 a gain stage coupled to receive an output signal of the bandpass filter; 
 a power detector coupled to receive an output signal of the gain stage; and 
 a threshold detector coupled to receive an output signal of the power detector, wherein an output signal of the threshold detector is received by the nonlinear auxiliary circuit. 
 
   
   
     20. The circuit of  claim 15 , wherein said linearization circuit comprises one of a feed-forward linearizer, a Cartesian feedback loop, a polar loop correction system and a digital adaptive pre-distortion system. 
   
   
     21. The circuit of  claim 20 , further comprising a feedback loop, wherein said feedback loop receives a portion of the output signal and outputs a non-linearity feedback signal to said nonlinear auxiliary circuit. 
   
   
     22. The circuit of  claim 21 , wherein said feedback loop further comprises a non-linearity detector that detects the amount of non-linearity in the output signal, wherein the non-linearity feedback signal is proportional to the amount of non-linearity detected by the non-linearity detector. 
   
   
     23. The circuit of  claim 22 , wherein said auxiliary nonlinear circuit increases a power level of said nonlinear auxiliary signal output in proportion to the non-linearity feedback signal. 
   
   
     24. A circuit for linearizing an input signal, comprising:
 a main circuit that receives the input signal and outputs a main output signal; 
 a nonlinear auxiliary output signal; 
 a combiner coupled to said main circuit and said nonlinear circuit that combines the main signal and the auxiliary signal to yield an output signal; and 
 a feedback loop that receives a portion of the output signal and outputs a non-linearity feedback signal to said auxiliary nonlinear circuit, 
 wherein the feedback loop includes a bandpass filter to pass adjacent or nearby channels of the output signal output from the combiner to determine if spectral leakage occurs in the adjacent or nearby channels. 
 
   
   
     25. A method for linearizing an input signal, comprising:
 processing the input signal with a main signal processing circuit; 
 processing the input signal with a non-linear circuit; 
 combining an output signal of the main signal processing circuit and the non-linear circuit to generate an output signal; 
 passing adjacent or nearby channels of the combined output signal through a bandpass filter; 
 determining if spectral leakage occurs in the adjacent or nearby channels; and 
 determining an adjustment to control parameters of the non-linear auxiliary circuit to change one of increase or decrease its non-linearity based on determining if spectral leakage occurs in the adjacent or nearby channels. 
 
   
   
     26. A method for improving signal quality in a signal processing system, comprising:
 (a) processing an input signal based on a transfer function H1; 
 (b) processing the input signal based on a transfer function H2; and 
 (c) subtracting the processed signals from steps (a) and (b), 
 wherein step (b) includes increasing non-linearity of transfer function H2 by an amount sufficient to substantially suppress at least one predetermined harmonic in the processed signal output from step (a) and at least first- and third-order harmonics in the processed signal output from step (b) when the processed signals are subtracted in step (c), and 
 wherein H 1 (X)=a 1 X+a 3 X 3  and H 2 (X)=b 1 X+b 3 X 3  and X is the transform of x(t), a 1 xa 3 <0, b 1 xb 3 <0, a 1 −a 3 is approximately a 1 , and b 1 −b 3  is approximately 0. 
 
   
   
     27. The method of  claim 26 , wherein the step of increasing the non-linearity of transfer function H2 includes: adjusting a loop control parameter which increases the non-linearity of transfer function H2. 
   
   
     28. The method of  claim 26 , wherein said at least one predetermined harmonic is a third-order harmonic. 
   
   
     29. A system for improving signal quality in a signal processing system, comprising:
 a first signal processing block which modifies an input signal based on a transfer function H1; 
 a second signal processing block which modifies the input signal based on a transfer function H2; 
 a combiner that combines the processed signals from the first and second signal processing blocks, wherein the second signal processing block increases non-linearity of transfer function H2 by an amount sufficient to substantially suppress at least one predetermined harmonic in the processed signal output from the first signal processing block and at least first- and third-order harmonics in the processed signal output from the second signal processing block when the processed signals are combined by the combiners 
 wherein H 1 (X)=a 1 X+a 3 X 3  and H 2 (X)=b 1 X+b 3 X 3  and X is the transform of x(t), a 1 xa 3 <0, b 1 xb 3 <0, a 1 −a 3  is approximately a 1 , and b 1 −b 3  is approximately 0. 
 
   
   
     30. The system of  claim 29 , wherein the second signal processing block adjusts a loop control parameter which increases the non-linearity of transfer function H2. 
   
   
     31. The system of  claim 29 , wherein said at least one predetermined harmonic is a third-order harmonic. 
   
   
     32. The system of  claim 29 , wherein the combiner is a subtractor. 
   
   
     33. The system of  claim 29 , wherein the second signal processing block increases the non-linearity of transfer function H2 by an amount sufficient to substantially suppress all harmonics in the processed signal output from the first signal processing block except a first-order harmonic, and to suppress at all harmonics in the processed signal output from the second signal processing block when the processed signals are subtracted in a subtractor. 
   
   
     34. A circuit for an initially at least partially nonlinear circuit; comprising:
 means for splitting an input signal into a first and second input signal; 
 means for determining the effect of the at least partially nonlinear circuit on a predetermined harmonic of said first input signal; and 
 a unit that receives said second input signal and modifies a second predetermined harmonic of said second input signal in a manner such that if the output of said unit and said at least partially nonlinear circuit are combined, the predetermined harmonic of said first input signal is at least partially suppressed, 
 wherein the determining means includes a bandpass filter to a pass adjacent or nearby channels of the combined output signal to determine if spectral leakage occurs in the adjacent or nearby channels. 
 
   
   
     35. The circuit of  claim 24 , wherein said feedback loop further comprises:
 a gain stage coupled to receive an output of the bandpass filter; 
 a power detector coupled to receive an output of the gain stage; and 
 a threshold detector coupled to receive an output of the power detector, wherein an output of the threshold detector is received by the nonlinear auxiliary circuit. 
 
   
   
     36. The circuit of  claim 34 , wherein the determining means further comprises:
 a gain stage coupled to receive an output of the bandpass filter; 
 a power detector coupled to receive an output of the gain stage; and 
 a threshold detector coupled to receive an output of the power detector, wherein an output of the threshold detector is received by the nonlinear auxiliary circuit. 
 
   
   
     37. A circuit for linearizing an input signal x(t), comprising:
 a main circuit that receives the input signal with a main transfer function of approximately H1 and outputs a main signal output; 
 a nonlinear auxiliary circuit that receives the input signal and has a nonlinear auxiliary transfer function of approximately H2 and outputs a nonlinear auxiliary signal output, wherein H 1 (X)=a 1 X+a 3 X 3  and H 2 (X)=b 1 X+b 3 X 3  and X is the transform of x(t), a 1 xa 3 <0, b 1 xb 3 <0, a 1 −a 3  is approximately a 1 , and b 1 −b 3  is approximately 0; 
 a combiner coupled to said main circuit and said nonlinear auxiliary circuit that combines said main signal and said auxiliary signal to yield an output signal; and 
 a feedback loop that receives a portion of the output signal and outputs a non-linearity feedback signal to said auxiliary nonlinear circuit, 
 wherein said main circuit comprises a linearization circuit.